A new study by the Hartford Hospital in Connecticut and the University of Iowa has found only "minimal" changes in a person's ability to properly operate a vehicle while under the influence of marijuana. Using a driving simulator, volunteers were subjected to situations that commonly lead to automobile accidents, once while sober, and again 30 minutes after smoking a marijuana cigarette. Researchers say they found virtually "no difference" in subjects' driving performance. Is driving while high really so dangerous? Here, a quick guide:

So smoking marijuana didn't affect drivers at all?Not exactly. Researchers found that "participants receiving active marijuana decreased their speed more so than those receiving a placebo cigarette" — that is, they drove more slowly. This confirms the results of a 2008 study, which found that "average speed was the most sensitive driving performance variable" when a person is high. The authors of the Hartford Hospital/University of Iowa study hypothesized that stoned drivers might be slowing down to compensate for some level of impairment.

What kind of driving scenarios were volunteers subjected to?The test included avoiding a driver who was entering an intersection illegally, having to decide whether to stop or go through a changing traffic light, responding to emergency vehicles, and maintaining a safe driving distance during an in-car auditory distraction.

Does this mean it's safe to drive while high on marijuana?No. The results "do not imply that it is safe to drive under the influence of marijuana," says Dr. Beth Anderson, who helped oversee the study. "Especially because we know people aren't just smoking marijuana. They do it while drinking. They do this when others are in the car, listening to music, talking on cell phones or texting. These behaviors distract drivers and are even more dangerous when someone has been using marijuana."

What, then, does the study tell us? That we need to learn more about the effects of this drug. This research, says Dr. Anderson, "merely shows us, we need to study this further. To create public policy and to keep people safe, you need to know what's really happening in the brain. You need to know the science behind it. You have to have the facts."